Device for electrolytically coating one side of metal strips

ABSTRACT

In a device for electrolytically coating one side of metal strips (2), the metal strips to be coated are guided around a rotary cathodic current roller (1), which they contact, and a partially cylindrical, insoluble anode (3) is arranged approximately concentrically around the current roller, at a distance thereof. The interval (4) between the section (21) of the strip guided on the current roller (1) and the anode (3) is delimited in the area of the strip edges (22) by seals (5) which can be oriented in a direction parallel to the axis of the roller. The electrolyte flows through the interval (4).

This is a 371 of PCT/93/0105 filed Oct. 22, 1993.

The invention relates to a device for electrolytically coating one sideof metal strips, in which the metal strips to be coated are contactinglyguided around a rotating cathodic current roller, and a partiallycylindrical, insoluble anode is arranged approximately concentricallyaround the current roller with a spacing from the latter, whereby theelectrolyte flows through the spacing.

In such a device, which is known from U.S. Pat. No. 3,900,383, the unitcomprising the current roller, the metal strip to be coated, the latterlooping around said roller by about 180°, and the partly cylindricalanode arranged with a spacing from said roller is completely immersed inan electrolyte bath in a tub. The continous contacting of the metalstrip to be coated, particularly a very thin strip, has the advantagethat voltage drops are avoided because the electrical field developsexclusively between the concentrically arranged anode and the cathodiccurrent roller or metal strip resting against the latter. However, thedrawback with said known device is the risk of coating the currentroller in the lateral zones not covered by the metal strip to be coated.In addition, there is the risk of electrolyte entering between thecurrent roller and the metal strip, leading to undesirable coatings.Particularly in connection with very thin strips, for example metalfoils, it is not possible to design the width of the current rollersmaller than the width of the strip, because the support of the latterwould be missing in that case. Also, with such a design, the projectinglateral strip would again be used for conducting current. This wouldresult in voltage drops and thus heating of the strip in the edge zones.

If the strip width is smaller than the roller width, the protruding zoneof the roller is galvanized. Since strips and foils of varying width arecoated in such installations, the rollers would have to be exchangedaccording to the width of the strip.

Also, a device of the type specified above is known from EP-OS 0 125707, in which the electrolyte is exclusively guided within the spacing(gap) between the partly cylindrical anode and the cylindrical cathodiccurrent roller, while maintaining a turbulent forced flow.

In this case too, there is the risk of undesirable coating of thecurrent roller, which obviously comes into contact with the electrolyte.The electrolyte is admitted via an inlet tube extending across the totalwidth of the current roller. With such an arrangement, the electrolytecan obviously exit from the gap between the anode and the current rolleralso on the face side and pass into a container arranged underneath.Therefore, the risk that electrolyte may enter between the metal stripto be coated and the current roller exists in this case as well.

The problem of the invention consists in proposing a device of the typespecified above, in which it is assured that the electrolyte does notcome into contact with the surface of the current roller.

The problem of the invention is solved with a device of the typespecified above, which device is characterized in that provision is madefor seals between the section of the strip guided on the current rollerand the anode, such seals being installed in each case within the zoneof the edge of the strip in the axially parallel direction. In this way,the space of the electrolyte is limited to the width of the strip, sothat wetting of the current roller with electrolyte is avoided. Inadaptation to the given width of the metal strip to be coated, thesealing can be installed on both sides of the strip, with a nearlyuncoated zone of the edge of the strip remaining, which, however, isseparated in the manufacture of such strips in any case.

The invention also comprises the proposal of lubricating the sealingside with blocking water against the section of the strip guided on thecurrent roller, with the intention to prevent any electrolyte that maypass through the sealing from coming into contact with the currentroller.

According to a further proposal of the invention, electrolyte suctiondevices can be arranged within the zone of the ends of the seals inconnection with one or a plurality of squeezer or reversing rollers, bywhich devices it is prevented that any electrolyte that may have beendragged along is wetting in the respective zones the current rollerbehind the seals.

A device according to the invention is explained in greater detail inthe following on an exemplified embodiment shown in general in thedrawing, in which:

FIG. 1 shows a section through a device for electrolytically coatingmetal strips on one side; and

FIG. 2 shows a section according to line A--A in FIG. 1.

A metal strip 2 to be coated on the outside is guided in the directionof the arrow around the driven cathodic current roller 1, contacting thelatter with a looping angle of greater than 180°. In this connection,the strip coming from the right according to FIG. 1, is guided via areversing roller 7 with as little spacing as possible from the currentroller, and passed on the opposite side via the reversing roller 7 afterit has been coated. A partially cylindrical anode 3 is arranged aroundthe current roller with the strip 2, whose section resting against saidroller is denoted by reference numeral 21. The electrolyte is passedthrough the spacing 4, said electrolyte entering on the right side ofFIG. 1 at reference numeral 41 and being withdrawn on the other side viathe outlet 42.

Laterally, the spacing 4 (gap) between the strip section 21 and theanode 3 is limited by the seals indicated by the reference numeral 5,which seals can be installed concentrically.

Said displaceable seals 5 each engage with the adjustable sealingsection 51 the strip edge zones 22 of the strip section 21 to be coated.A seal 52 arranged on the outside, for example a sealing bellows, sealsagainst the face side of the anode 3.

Preferably, a suction device 6 extending across the total width of thecurrent roller or only within the range of the seal ends, said devicebeing adjustable with the seals to the width of the strip, can bearranged above the electrolyte outlet upstream of the reversing roller 7or a suitable squeezing roller, for removing any electrolyte that mayhave been dragged along.

Within the zone of the seals 5, particularly, however, within the zoneof the sealing sections 22 resting against the strip section 21 to becoated, provision can be made for so-called blocking water lubricationsfrom the outside, by which any electrolyte that may exit is preventedfrom effectively wetting the adjacent zone of the current roller. Inthis way, any electrolyte that may exit is rinsed off or highly dilutedand consequently no longer effecting the coating.

We claim:
 1. Device for electrolytically coating a metal strip on oneside thereof comprisinga rotating cathodic current roller around whichthe metal strip section to be coated is contactingly guided; a partiallycylindrical, insoluble anode arranged approximately concentricallyaround the current roller with a spacing from the current roller; anelectrolyte for flowing through the spacing and having a coatingmaterial; means for preventing a deposition of the coating material onthe current roller in positions where no strip contact is achieved; andsaid means for preventing said deposition of coating-material comprisingseals arranged between the strip section guided on the current rollerand the anode, in each case within a zone of edges of the strip; andsaid seals having means for being adjustable in an axially paralleldirection to a width of the metal strip to be coated.
 2. Deviceaccording to claim 1,wherein the side of the seal against the stripsection guided on the current roller is lubricated with blocking water.3. Device according to claim 1,wherein electrolyte suction devices arearranged within the zone of the ends of the seals in connection with oneor a plurality of squeeze-off rollers.